Sequence and Phylogenetic Analyses of the Glucosyltransferase Gene of Mutans Streptococci Isolated from the Fruit Bat Oral Cavity

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The nucleotide sequence of the glucosyltransferase (GTF) gene was determined for the mutans streptococci isolated from the fruit bat oral cavity, Streptococcus dentirousetti NUM1303T, which encodes a GTF enzyme that synthesizes a water-insoluble glucan. The gtf of S. dentirousetti consisted of a 4,398-bp open reading frame that encoded for a 1,466 amino acid protein and was revealed to belong to the gtfI group. The deduced 38-amino acid sequence of the N-terminal was thought to be a signal peptide for the secretion of GTF-I enzyme, which has high similarity to known GTFs from other streptococci, and three major functional domains of GTFs : an N-terminal variable region, a conserved catalytic site for the hydrolysis of sucrose, and C-terminal repeating units for glucan binding. The percent homology of the amino acid sequence of the GTF-I from S. dentirousetti and Streptococcus orisuis is 99%, however, this score shows 78% when compared to Streptococcus sobrinus. Phylogenetic analysis suggested that this gtfI was closely related to Streptococcus orisuis based on the amino acid sequences from the other related streptococcal GTFs.